Communication device and system with ground potential difference compensation

ABSTRACT

A communication device for connection with a power source and a host device is provided. The communication device comprises a device controller and a converter circuit. The device controller is adapted for data communication with the host device and the converter circuit is configured to provide a virtual device ground at least to the device controller, so as to compensate a ground potential difference between the host device and the communication device.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent Application62/817,124, filed on Mar. 12, 2019 with the United States Patent andTrademark Office. The contents of this application are incorporatedherein for all purposes.

TECHNICAL FIELD

The present disclosure relates to the field of communication and inparticular to a communication device configured for connection with apower source and a host device.

BACKGROUND

A multitude of communication systems and protocols are being used today.Some systems are designed so that in addition to communication, it ispossible to transfer substantial amounts of power between two devices. Anotable such system is defined under the Universal Serial Bus (“USB”)standards. USB is ubiquitous today for conductor-based communicationlinks, but also for power transfer applications, such as mobile devicecharging.

Since its first version, USB has evolved from a data interface capableof supplying limited power in the range of 500 mA to a system, which asa main application, allows the transfer of substantial electrical power,while maintaining data communication functionality. Many of today'scomputing or telecommunication devices charge, or get their power, fromUSB ports contained in laptops, cars, aircraft, trains, or even USB wallsockets. USB has become the main power socket for devices such ascomputers, tablets, smart, phones, cell phones, MP3 players, and otherhand-held devices.

The USB Power Delivery (PD) specification Rev. 2.0 available from theUSB Implementers Forum, Inc., Beaverton, Oreg., enhances thefunctionality of USB by providing a more flexible power delivery alongwith data communication over a single cable. Its aim is to operate withand build on the existing USB ecosystem.

With USB Power Delivery (USB-PD), USB-PD capable devices drawsignificantly higher currents from the power source than previous USBdevices due to an increased power budget per port. While previousspecifications allowed a maximum power draw of 15 W per port, the USB-PDallows up to 100 W of electrical power per port. This increase is quitesignificant.

SUMMARY

The present inventor has ascertained that in some applications, avoltage drop on a ground connection between two devices due to thepresence of high currents, such as for example when charging overUSB-PD, can cause a significant ground shift between the two devices. Insome instances, the ground shift can hinder proper communication, or ina worst case scenario, make communication between the two devicesimpossible.

A known method to avoid this issue is to minimize the ohmic resistanceby using larger copper wire diameters or shorter cable lengths. Thismethod however is costly and limits wiring possibilities.

Thus, a need exists to improve a corresponding communication system andcommunication device to allow proper communication irrespective of anypower transfer that may cause a ground shift.

This need is addressed by a communication device, a communication systemwith a communication device, and a method of communication according tothe independent claims. The dependent claims and the followingspecification discuss embodiments of the invention.

According to one aspect of the invention, a communication device isprovided. The communication device is configured for connection with apower source and a host device and comprises at least a devicecontroller, adapted for data communication with the host device. Thecommunication device further comprises a converter circuit, whichconverter circuit is configured to provide a virtual device ground atleast to the device controller to compensate a ground potentialdifference between the host device and the communication device.

An underlying idea of the above aspect is to compensate any eventualground shift between the host device and the communication device usinga virtual ground on the side of the communication device. This avoidsthe need to use larger copper wire diameters or shorter cable lengths,which allows a significantly increased flexibility. In addition, theprovision of the virtual ground on the side of the communication devicemay in some embodiments be independent of the implementation of the hostdevice, which may provide cost benefits.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantages of the currentinvention will become apparent from the following discussion of variousembodiments. In the FIGS.,

FIG. 1 shows an exemplary block diagram of a USB communication system;

FIG. 2 shows an exemplary block diagram of an embodiment of acommunication system and a communication device;

FIG. 3 shows an equivalent circuit diagram of the embodiment of FIG. 2 ;

FIG. 4 shows an equivalent circuit diagram of another embodiment; and

FIG. 5 shows an exemplary block diagram of another embodiment of acommunication system and a communication device.

DETAILED DESCRIPTION

Technical features described in this application can be used toconstruct various embodiments of communication devices and communicationsystems. Some embodiments of the invention are discussed so as to enableone skilled in the art to make and use the invention.

In one aspect, a communication device is provided. The communicationdevice may be used in a communication system and is configured forconnection with a power source and a host device. The communicationdevice comprises at least a device controller, adapted for datacommunication with the host device. The communication device furthercomprises a converter circuit, which converter circuit is configured toprovide a virtual device ground at least to the device controller tocompensate a ground potential difference between the host device and thecommunication device.

As will be apparent from the preceding, the present aspect provides avirtual device ground, i.e., a local ground at least for the devicecontroller. The potential of the virtual device ground may be set by theconverter circuit to compensate for any eventual potential difference,i.e., ground shift between the communication device and the host device,resulting in a more stable connection between the devices to enableimproved communication.

The communication device may be of any suitable type. In someembodiments, the communication device may be adapted for use with one ormore serial communication protocols, such as one or more of USB,Thunderbolt, CAN bus, FireWire, and Ethernet.

For example, the communication device may be USB device of any deviceclass or a USB hub. In the aforementioned cases, the device controllerin some embodiments may be a USB device function controller or a USB hubcontroller. In some embodiments, the communication device is configuredto communicate with the host device using the USB 2.0 protocol or ahigher protocol version. In some embodiments, the communication deviceis a “Breakout Box” or a “Media Box”, e.g., for vehicles. In someembodiments, the host device is a head unit.

The communication device of the present aspect is configured forconnection to a power source and a host device. In some embodiments, thepower source and the host device are integrated with each other. Inalternative embodiments, the power source and the host device areseparated from each other. In some embodiments, the power sourceprovides an electrical operating power of at least 15 W to thecommunication device. The operating power may be used in someembodiments for operational needs of the communication device, thecharging of a battery of the communication device, and/or for poweringfurther downstream devices, connected to one or more downstream ports ofthe communication device. The host device may be of any suitable typefor data communication with the communication device, e.g., digitalcommunication. Although the terms ‘host device’ and ‘USB device’ areused in line with the usual terminology of the Universal Serial Busstandard, it is noted that the logical functionality may depart from theUSB terminology in some embodiments. For example, the communicationdevice may have the functionality of a USB host and the host device mayhave the functionality of USB device.

As discussed in the preceding, the communication device of this aspectcomprises the converter circuit to provide a virtual device ground atleast to the device controller to compensate for a ground shift betweenthe host device and the communication device. In other words, theconverter circuit may compensate a voltage drop on a ground connectionbetween the host device and the communication device due to lineimpedance. In some embodiments, the converter circuit is provided aspart of the device which consumes power.

The converter circuit may be of any suitable type. In some embodiments,the converter circuit comprises a switched-mode power supply. In someembodiments, the converter circuit comprises one of a buck converter, aboost converter, a buck/boost converter, and any other suitableconverter.

In some embodiments, the converter circuit is a buck converter withpositive output voltage. This may be more effective in terms of cost andsize than generating negative voltages. In some embodiments, theconverter circuit is used to shift its internal ground level downwards.

In some embodiments, the converter comprises a sense input (sense line)for connection to a ground potential (level) of the host device and/orthe power source. In the present context, the term ‘ground potential ofthe host’ is understood as the electrical potential of the signal groundon the side of the host device, i.e., the signal ground, used for datacommunication with the communication device. In some embodiments, theconverter circuit comprises a compensator to control the virtual deviceground. The compensator may be of any suitable type of digital or analogcircuitry. For example, the compensator may be a microcontroller withsuitable programming. In some embodiments, the compensator is a digital3P3Z compensator. In some embodiments, the compensator is connected withthe sense input to determine the ground potential of the host device. Insome embodiments, the compensator is connected with a switched-modepower supply, such as for example a buck converter, of the convertercircuit, to control the virtual device ground.

In some embodiments, the compensator is configured to, using the senseinput, control the virtual device ground, so that a difference betweenthe virtual device ground and the ground potential of the host device isreduced. Alternatively, it is possible to determine the ground potentialat the power source, in particular if the impedance of a groundconnection between power source and the host device is so small that theresulting voltage drop can be neglected compared to a maximum groundshift threshold of 125 mV, as discussed in more detail in the following.

In some embodiments, the compensator is configured to control thevirtual device ground to match the ground level of the host device(+−125 mV).

The compensator in some embodiments may be configured to control theconverter circuit based on a pre-determined impedance of the signalground between host device and communication device. The pre-determinedimpedance may for example be determined during assembly and thenprogrammed into a memory of the compensator. In some embodiments, thecompensator is configured to determine the impedance during power-on bymeasurement. For example, the compensator may draw current pulses fromthe power source and determine changes of an internal ground potentialcompared with the ground potential of the host.

In some embodiments, the compensator may be configured to determine anoverall power consumption of the communication device, e.g., includingany connected downstream devices. In some embodiments, the compensatormay include power consumption measurement circuitry. If the impedance ofthe ground connection and the overall power consumption of thecommunication device is known, the sense input, as described in thepreceding, may be omitted.

In some embodiments, the communication device further comprises a secondconverter circuit, which second converter circuit is connected with thepower source and configured to provide an internal supply voltage. Theinternal supply voltage in some embodiments may be provided to thedevice controller. Alternatively, or additionally, the internal supplyvoltage may be provided to further components of the communicationdevice and/or to one or more connected downstream devices. In someembodiments, the internal supply voltage is higher than a voltagesupplied by the power source to the communication device.

In some embodiments, the second converter circuit is a switched-modepower supply, such as for example, a boost converter.

In some embodiments, the second converter circuit comprises a groundterminal, which ground terminal is not connected to the virtual deviceground. In other words, the ground of the second converter circuitduring use is connected to the ground of the power source, whichprevents the second converter circuit from loading the first convertercircuit.

In some embodiments, the communication device is a USB hub. In someembodiments, the USB hub comprises one or more downstream ports. In someembodiments, the virtual device ground is provided to the one or moredownstream ports.

In some embodiments, one or more of the downstream ports have anassociated downstream power converter. The downstream power convertermay for example be a switched-mode power supply, such as a buckconverter. In some embodiments, the downstream power converter isconnected to the virtual device ground.

One or more downstream ports may in some embodiments share oneassociated downstream power converter. Alternatively, and in someembodiments, one or more of the downstream ports each have a dedicatedassociated downstream power converter. In some embodiments, a dedicateddownstream power converter is arranged per downstream port.

In a second aspect, a communication system with a host device and acommunication device is provided. The communication device of thecommunication system being configured for connection with (or isconnected to) the host device and a power source. The communicationdevice comprises at least a device controller, adapted for datacommunication with the host device, and a converter circuit. Theconverter circuit is configured to provide a virtual device ground atleast to the device controller to compensate a ground potentialdifference between the host device and the communication device.

The communication device and the host device may in some embodiments beconfigured as discussed in the preceding with reference to the firstaspect. With respect to terms used in the explanation of the secondaspect and their definitions, reference is made to the first aspect.

According to a third aspect, a method of communication in acommunication system with a host device and a communication device isprovided. The method of the present aspect comprises the steps of:

providing a virtual ground at least to a device controller of thecommunication device;

controlling the virtual ground, so that a difference of potentialbetween the virtual device ground and a ground potential of the hostdevice is reduced; and

communicating between the host device and the communication device.

The communication device and the host device may in some embodiments beconfigured as discussed in the preceding with reference to the first andsecond aspects. With respect to terms used in the explanation of thethird aspect and their definitions, reference is made to the firstaspect.

It is noted that the communication device, communication system, and/orthe method of communication as discussed in the preceding may in someembodiments be used in a vehicle, airplane, train or ship, withoutlimitation. According to another aspect, a vehicle with a communicationdevice or a communication system, as described in the preceding, isprovided.

Reference will now be made to the drawings in which further embodimentsare discussed and in which various elements will be given numericaldesignations.

Specific references to components, process steps, and other elements arenot intended to be limiting. Further, it is understood that like partsbear the same or similar reference numerals when referring to alternatefigures. It is further noted that the FIGS. are schematic and providedfor guidance to the skilled reader and are not necessarily drawn toscale. Rather, the various drawing scales, aspect ratios, and numbers ofcomponents shown in the FIGS. may be purposely distorted to make certainfeatures or relationships easier to understand.

The following discussion of further embodiments relates to UniversalSerial Bus (“USB”) applications. USB has evolved from a data interfacecapable of supplying limited power to a primary provider of power with adata interface. Today many devices charge or get their power from USBports contained in laptops, cars, aircraft or even wall sockets. USB hasbecome a ubiquitous power socket for many small devices such as cellphones, MP3 players and other hand-held devices. Users need USB tofulfil their requirements not only in terms of data but also to providepower to, or charge, their devices simply, often without the need toload a driver, in order to carry out “traditional” USB functions.

The USB Power Delivery (PD) specification improves functionality of USBby providing more flexible power delivery along with data over a singlecable. Its aim is to operate with, and build on, the existing USBecosystem.

The USB-PD specification allows up to 100 W per port. USB-PD capabledevices may thus draw significantly higher currents from the powersource than previous USB devices (increased power budget per port: 15W→100 W).

With USB-PD solutions providing higher power levels, the voltage drop onthe ground line may become a serious issue. This invention addresses theground shift issue between a USB host device (such as a “Head Unit” in avehicle) and a USB communication device (such as a USB-PD capable USB“MediaBox”, or USB hub, without limitation).

When the USB communication device draws power, its internal ground isshifted upwards due to the voltage drop on the ground wire between thepower source and the USB communication device. If this ground shiftexceeds a threshold of 125 mV, communication between the host device,which typically shares ground with the power source, and thecommunication device will be disconnected.

In some embodiments, a virtual ground is employed to solve the issue ofa disconnection. This solution is less complex and easier to implementthen using an alternative physical layer or tunneling data via adifferent protocol. The solution has a cost advantage compared to amodified cable harness (more copper) and saves weight which is desiredin mobile applications (automotive, train, ship, airplane).

FIG. 1 shows an exemplary block diagram of a communication system 1,i.e., in this example a USB 3.x system, arranged in a vehicle (notshown). A host device 2 in the form of a “head unit” is connected with acommunication device 4, i.e., in the example of FIG. 1 , in the form ofa “USB breakout box”. The communication device 4 comprises a devicecontroller 5, which in the shown setup provides the functionality of aUSB hub and which allows for connection to one or more further USBdevices (not shown), such as a smart phone, tablet, or laptop, throughdownstream ports 6 a-6 c.

The communication device 4 allows for operation in accordance with theUSB-PD specification and provides an operating power of up to 100 W eachto the downstream ports 6 a-6 c. To allow this, the communication device4 according to the example of FIG. 1 is connected to the vehicle's powersource, i.e., herein a 12V battery 3, and comprises three buck/boostconverters 7 a-7 c, associated with the downstream ports 6 a-6 c. Thebuck/boost converters 7 a-7 c are arranged to provide voltages ofbetween 5V and 20V to the downstream ports 6 a-6 c according to thevoltage, requested by a USB device (not shown), when connected to arespective downstream port 6 a-6 c.

As will be apparent, the ground wire connection 13 between thecommunication device 4 and the host device 2 and its cable resistancewill inevitably cause a voltage drop U_(drop). Accordingly, the groundpotential of line GND1 at the host device 2, and at the return ofbattery 3, will not match the ground potential of line GND2 of thecommunication device 4. It is noted that the internal ground connectionof the communication device 4 and the ground connection between battery3 and host device 2 are considered to be ideal, i.e., having anegligible impedance only. Accordingly, U_(drop) is also present betweenthe GND pin of the head unit 2 and the GND pin of the device controller5, as shown in FIG. 1 . The embodiments herein are equally capable ofhandling a voltage drop on the ground wire connection between battery 3and host device 2.

The voltage drop U_(drop) will increase with the power drawn from thebattery 3 during operation, i.e., when further USB devices are connectedto the downstream ports 6 a-6 c.

If the voltage drop between the host-side ground, i.e., GND1 and theground GND2 at the device-side is higher than 125 mV, the connectionbetween the host device 2 and the communication device 4 may bedisconnected in line with the requirements of the USB SpecificationRevision 2.0, Section 7.2.2. This situation may arise in particular whensignificant power is drawn at the downstream ports 6 a-6 c.

FIG. 2 shows an exemplary block diagram of an embodiment of acommunication system 1 a and a communication device 4 a. In contrast tothe setup of FIG. 1 , the device controller 5 in this embodiment isconnected to a virtual device ground IGND of the communication device 4a. The virtual device ground IGND is provided by a converter circuit 8,which in the present embodiment, comprises a switched-mode power supply,namely a buck converter 9 and a compensator 14.

The communication device 4 a of FIG. 2 uses the converter circuit 8 toset the potential of IGND to be approximately equal to the potential ofGND1 independent of the voltage drop U_(drop). The compensator 14 isconnected with a sense line 10 to the electric potential of GND1, whichprovides a particularly beneficial dynamic behavior. In the presentembodiment, compensator 14 is a digital 3-pole 3-zero (3P3Z)compensator, realized as a microcontroller, although it is noted thatany other digital or analog compensator may be used. The compensator 14is configured so that buck converter 9 provides a compensation voltageU_(comp), which is of same value but of opposite polarity to U_(drop),and thus offsets U_(drop).

As will be further apparent from FIG. 2 , instead of buck/boostconverters 7 a-7 c used in the setup of FIG. 1 , the present embodimentemploys a combination of a second power converter, i.e., a switched-modepower supply, namely a boost converter 20, with dedicated downstreampower converters 21 a-21 c, associated with the respective downstreamports 6 a-6 c. The boost converter 20 in this embodiment provides afixed voltage U₂ with reference to potential IGND. Capacitor 12stabilizes this voltage. It is noted that the virtual device ground IGNDis also provided to the downstream power converters 21 a-21 c and thedownstream ports 6 a-6 c.

The dedicated downstream power converters 21 a-21 c are buck convertersand are arranged to reduce the voltage as required by respective USBdevices (not shown), connected to the downstream ports 6 a-6 c. Whilethree dedicated downstream power (buck) converters 21 a-21 c andassociated downstream ports 6 a-6 c are illustrated, the communicationdevice 4 a may have more than, or less than, three converters andassociated ports, depending on the application.

In the embodiment of FIG. 2 , the load of the buck converter 9 in termsof electrical power is as follows:P _(Buck) =P _(Load) *U _(comp) /U ₂ −U _(comp),

where P_(Load) is the power of the load, applied to the buck converter 9by the downstream ports 6 a-6 c during use. The power of the load seenby the boost converter circuit 20 can in this case be expressed as:P _(Boost) =P _(Load) *U ₂ /U ₂ −U _(comp)  (1)

An equivalent circuit diagram is shown in FIG. 3 . As can be seen fromthe FIG., in this example, the ground terminal of the boost convertercircuit 20 is not connected to the virtual device ground IGND, butconnected to the ground of battery 3. For clarity, it is noted that thedownstream power converters 21 a-21 c and associated downstream ports 6a-6 c are shown in FIGS. 3 and 4 as a summarized load P_(Load).

FIG. 4 shows a second embodiment in an equivalent circuit diagram, whichillustrates a further topology option of connecting the buck converter 9and the boost converter 20 of FIG. 2 .

The load of the buck converter 9 in the arrangement of FIG. 4 can beexpressed as:P _(Buck) =P _(Load) *U _(comp) /U ₁ −U _(comp)  (2)

While the topology option of FIG. 4 may be applied to the setup, shownin FIG. 2 , a comparison of the two preceding equations, i.e. eq. (1)and eq. (2) shows that the overall load of the buck converter 9 in theembodiment of FIG. 4 is higher, since the battery voltage U₁ in thedenominator of eq. 2 is lower than the boost converter output voltage U₂in eq. (1).

Accordingly, while the setup of FIG. 4 may provide a relatively simplesetup, losses at the buck converter 9 may be somewhat higher, comparedwith the topology option of FIG. 3 .

It is noted that the communication system 1 a of FIG. 2 could be adaptedto use buck/boost converters instead of the combination of boostconverter 20 and the buck converters 21 a-21 c. A correspondingembodiment is shown in FIG. 5 . The system 1 b and communication device4 b of FIG. 5 corresponds to the system 1 a and communication device 4 aof FIG. 2 , with the exception that the boost converter 20 has beenremoved and that instead of buck converters 21 a-21 c buck/boostconverters 51 a-51 c, typically embodied by 4 switch converters, areused for all downstream ports 6 a-6 c.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, such illustration and descriptionare to be considered illustrative or exemplary and not restrictive; theinvention is not limited to the disclosed embodiments.

Other variations to the disclosed embodiments can be understood andeffected by those skilled in the art in practicing the claimedinvention, from a study of the drawings, the disclosure, and theappended claims. In the claims, the word “comprising” does not excludeother elements or steps, and the indefinite article “a” or “an” does notexclude a plurality. A single processor, module or other unit mayfulfill the functions of several items recited in the claims.

The mere fact that certain measures are recited in mutually differentdependent claims or embodiments does not indicate that a combination ofthese measures cannot be used to advantage. Programming may bestored/distributed on a suitable medium, such as an optical storagemedium or a solid-state medium supplied together with or as part ofother hardware, but may also be distributed in other forms, such as viathe Internet or other wired or wireless telecommunication systems. Anyreference signs in the claims should not be construed as limiting thescope.

What is claimed is:
 1. A communication device for connection with apower source and a host device, the communication device comprising: adevice controller circuit for data communication with the host device;one or more downstream ports for connecting one or more respectivedevices, different from the host device; and a converter circuit toprovide a virtual device ground at least to the device controllercircuit and to the one or more downstream ports to compensate a groundpotential difference between the host device, the device controllercircuit, and the one or more downstream ports of the communicationdevice; wherein the converter circuit comprises a compensator and asense input, the sense input connected to the compensator, the senseinput for connection to a ground potential of the host device and thecompensator to control the virtual device ground based on a comparisonof the ground potential of the host device with a ground potential ofthe communication device.
 2. The communication device of claim 1,wherein the compensator to control the virtual device ground so that adifference of potential between the virtual device ground and the groundpotential of the host device is reduced.
 3. The communication device ofclaim 1, wherein the compensator to control the virtual device ground tomatch the ground potential of the host device.
 4. The communicationdevice of claim 1, wherein the converter circuit comprises aswitched-mode power supply.
 5. The communication device of claim 4,wherein the switched-mode power supply is a buck converter.
 6. Thecommunication device of claim 1, comprising a second converter circuit,which second converter circuit for connection to the power source and toprovide an internal supply voltage for the communication device.
 7. Thecommunication device of claim 6, wherein the internal supply voltage ishigher than a voltage provided by the power source.
 8. The communicationdevice of claim 6, wherein the second converter circuit is aswitched-mode power supply.
 9. The communication device of claim 6,wherein the second converter circuit comprises a ground terminal, whichground terminal is not connected to the virtual device ground.
 10. Thecommunication device of claim 1, wherein the communication device is aUSB device or a USB hub.
 11. The communication device of claim 1,wherein one or more of the downstream ports have an associateddownstream power converter.
 12. The communication device of claim 11,wherein the downstream power converter is connected with the virtualdevice ground.
 13. The communication device of claim 11, wherein foreach of the downstream ports, a dedicated associated downstream powerconverter is provided.
 14. A communication system with a host device anda communication device, the communication device for connection with thehost device and with a power source, the communication devicecomprising: a device controller circuit for data communication with thehost device; one or more downstream ports for connecting one or morerespective devices, different from the host device; and a convertercircuit to provide a virtual device ground at least to the devicecontroller circuit and to the one or more downstream ports to compensatea ground potential difference between the host device, the devicecontroller circuit, and the one or more downstream ports of thecommunication device; wherein the converter circuit comprises acompensator and a sense input, the sense input connected to thecompensator, the sense input for connection to a ground potential of thehost device and the compensator to control the virtual device groundbased on a comparison of the ground potential of the host device with aground potential of the communication device.
 15. A method ofcommunication in a communication system with a host device and acommunication device, the method comprising: sensing a ground potentialat the host device using a sense input for connection to a groundpotential of the host device; providing a virtual ground to a devicecontroller circuit of the communication device and to one or moredownstream ports, which downstream ports are for connecting one or morerespective devices, different from the host device; controlling thevirtual ground based on a comparison of the sensed ground potential atthe host device with a ground potential of the communication device, sothat a difference of potential between the virtual ground and the groundpotential at the host device is reduced; and communicating between thehost device and the communication device.
 16. The communication deviceof claim 1, wherein the sense input comprises a dedicated sense linethat is connectable to the ground potential of the host device.
 17. Thecommunication device of claim 1, wherein the compensator is a digital3P3Z compensator.